Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. In some embodiments, the processing circuitry decodes prediction information of a current block in a current coding from a coded video bitstream. The prediction information is indicative of an intra block copy mode. Then, the processing circuitry determines a block vector that points to a reference block in a same picture as the current block. The reference block is restricted within a coding region with reconstructed samples buffered in a reference sample memory. The coding region is one of multiple predefined regions of a coding tree unit (CTU). Then, the processing circuitry reconstructs at least a sample of the current block based on the reconstructed samples of the reference block that are retrieved from the reference sample memory.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 62/774,148, “CONSTRAINTS ON REFERENCE BLOCKLOCATIONS FOR INTRA BLOCK COPY” filed on Nov. 30, 2018, and U.S.Provisional Application No. 62/790,454, “INTRA PICTURE BLOCKCOMPENSATION BUFFER REUSE WITH NON SQUARE BLOCK PARTITIONS” filed onJan. 9, 2019. The entire disclosures of the prior applications arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. In someembodiments, the processing circuitry decodes prediction information ofa current block in a current coding from a coded video bitstream. Theprediction information is indicative of an intra block copy mode. Then,the processing circuitry determines a block vector that points to areference block in a same picture as the current block. The referenceblock is restricted within a coding region with reconstructed samplesbuffered in a reference sample memory. The coding region is one ofmultiple predefined regions of a coding tree unit (CTU). Then, theprocessing circuitry reconstructs at least a sample of the current blockbased on the reconstructed samples of the reference block that areretrieved from the reference sample memory.

In some examples, the coding region has a square shape. In an example,the CTU is configured to have 128 samples by 128 samples of a lumacomponent

In an embodiment, the reference sample memory is configured to updatesamples buffered in the reference sample memory in a unit of the codingregion.

In some embodiments, the processing circuitry checks whether multiplecorners of the reference block are within the coding region.

In an example, when the CTU contains 128×128 luma samples, the codingregion size is 64×64 luma samples in size. In another example, when theCTU contains less than 128×128 luma samples, the coding region is thesame as the CTU in size.

In some embodiments, the processing circuitry moves the reference blockinto the coding region when the reference block is partially in thecoding region before the moving. In an example, the processing circuitrymoves the reference block in a direction to reduce a distance betweenthe reference block and the current block. In another example, theprocessing circuitry moves the reference block in a direction thatincreases a percentage of reference samples in the coding region.

In some embodiments, the processing circuitry uses information of afirst reference sample that is in the coding region as information of asecond reference sample that is out of the coding region when thereference block is partially in the coding region. In some examples,flexible block partition is prohibited in a partition of the CTU.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system (100) in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 6 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 7 shows an example of intra block copy according to an embodimentof the disclosure.

FIGS. 8A-8D show examples of reference sample memory updates, andeffective search ranges for the intra block copy mode according to anembodiment of the disclosure.

FIGS. 9A-9H show some examples of partitions that can result innon-square blocks.

FIGS. 10A and 10B show two examples of coding orders and referencesample memory usage.

FIGS. 11A and 11B show examples of samples in a reference block comingfrom two different coding regions.

FIGS. 12A-12F show examples of reference samples memory reusestrategies.

FIGS. 13A-13F show examples of an update process according to someembodiments of the disclosure.

FIG. 14 shows a flow chart outlining a process example according to someembodiments of the disclosure.

FIG. 15 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. Thecommunication system (100) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (150). Forexample, the communication system (100) includes a first pair ofterminal devices (110) and (120) interconnected via the network (150).In the FIG. 1 example, the first pair of terminal devices (110) and(120) performs unidirectional transmission of data. For example, theterminal device (110) may code video data (e.g., a stream of videopictures that are captured by the terminal device (110)) fortransmission to the other terminal device (120) via the network (150).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (120) may receive the codedvideo data from the network (150), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (100) includes a secondpair of terminal devices (130) and (140) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (130) and (140)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (130) and (140) via the network (150). Eachterminal device of the terminal devices (130) and (140) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (130) and (140), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 1 example, the terminal devices (110), (120), (130) and(140) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (150) represents any number ofnetworks that convey coded video data among the terminal devices (110),(120), (130) and (140), including for example wireline (wired) and/orwireless communication networks. The communication network (150) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(150) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating forexample a stream of video pictures (202) that are uncompressed. In anexample, the stream of video pictures (202) includes samples that aretaken by the digital camera. The stream of video pictures (202),depicted as a bold line to emphasize a high data volume when compared toencoded video data (204) (or coded video bitstreams), can be processedby an electronic device (220) that includes a video encoder (203)coupled to the video source (201). The video encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (204) (or encoded video bitstream (204)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (202), can be stored on a streamingserver (205) for future use. One or more streaming client subsystems,such as client subsystems (206) and (208) in FIG. 2 can access thestreaming server (205) to retrieve copies (207) and (209) of the encodedvideo data (204). A client subsystem (206) can include a video decoder(210), for example, in an electronic device (230). The video decoder(210) decodes the incoming copy (207) of the encoded video data andcreates an outgoing stream of video pictures (211) that can be renderedon a display (212) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (204),(207), and (209) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (220) and (230) can includeother components (not shown). For example, the electronic device (220)can include a video decoder (not shown) and the electronic device (230)can include a video encoder (not shown) as well.

FIG. 3 shows a block diagram of a video decoder (310) according to anembodiment of the present disclosure. The video decoder (310) can beincluded in an electronic device (330). The electronic device (330) caninclude a receiver (331) (e.g., receiving circuitry). The video decoder(310) can be used in the place of the video decoder (210) in the FIG. 2example.

The receiver (331) may receive one or more coded video sequences to bedecoded by the video decoder (310); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (301), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (331) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (331) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween the receiver (331) and an entropy decoder/parser (320) (“parser(320)” henceforth). In certain applications, the buffer memory (315) ispart of the video decoder (310). In others, it can be outside of thevideo decoder (310) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (310), forexample to combat network jitter, and in addition another buffer memory(315) inside the video decoder (310), for example to handle playouttiming. When the receiver (331) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (315) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (315) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (310).

The video decoder (310) may include the parser (320) to reconstructsymbols (321) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (310),and potentially information to control a rendering device such as arender device (312) (e.g., a display screen) that is not an integralpart of the electronic device (330) but can be coupled to the electronicdevice (330), as was shown in FIG. 3. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (320) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (320) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (320) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (315), so as tocreate symbols (321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (310)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). The scaler/inversetransform unit (351) can output blocks comprising sample values, thatcan be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (358). The currentpicture buffer (358) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(355), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (352) has generated to the outputsample information as provided by the scaler/inverse transform unit(351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (351) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (357) from where themotion compensation prediction unit (353) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (353) in the form of symbols (321) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (357) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (356) as symbols (321) from the parser (320), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory (357) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (320)), the current picture buffer (358) can becomea part of the reference picture memory (357), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (310) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (331) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (310) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 4 shows a block diagram of a video encoder (403) according to anembodiment of the present disclosure. The video encoder (403) isincluded in an electronic device (420). The electronic device (420)includes a transmitter (440) (e.g., transmitting circuitry). The videoencoder (403) can be used in the place of the video encoder (203) in theFIG. 2 example.

The video encoder (403) may receive video samples from a video source(401) (that is not part of the electronic device (420) in the FIG. 4example) that may capture video image(s) to be coded by the videoencoder (403). In another example, the video source (401) is a part ofthe electronic device (420).

The video source (401) may provide the source video sequence to be codedby the video encoder (403) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (401) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (401) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (403) may code andcompress the pictures of the source video sequence into a coded videosequence (443) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (450). In some embodiments, the controller(450) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (450) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (450) can be configured to have other suitablefunctions that pertain to the video encoder (403) optimized for acertain system design.

In some embodiments, the video encoder (403) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (430) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (433)embedded in the video encoder (403). The decoder (433) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (434). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (434) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder, such as the video decoder (310), which has alreadybeen described in detail above in conjunction with FIG. 3. Brieflyreferring also to FIG. 3, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (445) and the parser (320) can be lossless, the entropy decodingparts of the video decoder (310), including the buffer memory (315), andparser (320) may not be fully implemented in the local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (430) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (432) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (433) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (434). In this manner, the video encoder(403) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new picture to be coded, the predictor(435) may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the source coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder (445)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (403) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the video encoder (403).During coding, the controller (450) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (403) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (403) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The source coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 5 shows a diagram of a video encoder (503) according to anotherembodiment of the disclosure. The video encoder (503) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (503) is used in theplace of the video encoder (203) in the FIG. 2 example.

In an HEVC example, the video encoder (503) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (503) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (503) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(503) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (503) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 5 example, the video encoder (503) includes the interencoder (530), an intra encoder (522), a residue calculator (523), aswitch (526), a residue encoder (524), a general controller (521), andan entropy encoder (525) coupled together as shown in FIG. 5.

The inter encoder (530) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (522) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (522) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (521) is configured to determine general controldata and control other components of the video encoder (503) based onthe general control data. In an example, the general controller (521)determines the mode of the block, and provides a control signal to theswitch (526) based on the mode. For example, when the mode is the intramode, the general controller (521) controls the switch (526) to selectthe intra mode result for use by the residue calculator (523), andcontrols the entropy encoder (525) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(521) controls the switch (526) to select the inter prediction resultfor use by the residue calculator (523), and controls the entropyencoder (525) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (523) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (522) or the inter encoder (530). Theresidue encoder (524) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (524) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (503) also includes a residuedecoder (528). The residue decoder (528) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (522) and theinter encoder (530). For example, the inter encoder (530) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (522) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (525) is configured to format the bitstream toinclude the encoded block. The entropy encoder (525) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (525) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 6 shows a diagram of a video decoder (610) according to anotherembodiment of the disclosure. The video decoder (610) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (610) is used in the place of the videodecoder (210) in the FIG. 2 example.

In the FIG. 6 example, the video decoder (610) includes an entropydecoder (671), an inter decoder (680), a residue decoder (673), areconstruction module (674), and an intra decoder (672) coupled togetheras shown in FIG. 6.

The entropy decoder (671) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (672) or the inter decoder (680), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (680); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (672). The residual information can be subject to inversequantization and is provided to the residue decoder (673).

The inter decoder (680) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (672) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (673) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (673) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (671) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (674) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (673) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (203), (403), and (503), and thevideo decoders (210), (310), and (610) can be implemented using anysuitable technique. In an embodiment, the video encoders (203), (403),and (503), and the video decoders (210), (310), and (610) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (203), (403), and (403), and the videodecoders (210), (310), and (610) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide techniques to constrain referenceblock locations for intra block copy mode, and provide techniques tore-use intra picture block compensation buffer with non-square blockpartitions.

Block based compensation can be used for inter prediction and intraprediction. For the inter prediction, block based compensation from adifferent picture is known as motion compensation. For intra prediction,block based compensation can also be done from a previouslyreconstructed area within the same picture. The block based compensationfrom reconstructed area within the same picture is referred to as intrapicture block compensation, current picture referencing (CPR) or intrablock copy (IBC). A displacement vector that indicates the offsetbetween the current block and the reference block in the same picture isreferred to as a block vector (or BV for short). Different from a motionvector in motion compensation, which can be at any value (positive ornegative, at either x or y direction), a block vector has a fewconstraints to ensure that the reference block is available and alreadyreconstructed. Also, in some examples, for parallel processingconsideration, some reference area that is tile boundary or wavefrontladder shape boundary is excluded.

The coding of a block vector could be either explicit or implicit. Inthe explicit mode (similar to advanced motion vector prediction (AMVP)mode in inter coding), the difference between a block vector and itspredictor is signaled; in the implicit mode, the block vector isrecovered from a predictor (referred to as block vector predictor), in asimilar way as a motion vector in merge mode. The resolution of a blockvector, in some implementations, is restricted to integer positions; inother systems, the block vector is allowed to point to fractionalpositions.

In some examples, the use of intra block copy at block level, can besignaled using a block level flag, that is referred to as an IBC flag.In an embodiment, the IBC flag is signaled when the current block is notcoded in the merge mode. In another embodiment, the IBC flag is signaledusing a reference index approach. The current picture under decoding isthen treated as a reference picture. In an example, such a referencepicture is put in the last position of a list of reference pictures.This special reference picture is also managed together with othertemporal reference pictures in a buffer, such as decoded picture buffer(DPB).

There are also some variations for intra block copy, such as flippedintra block copy (the reference block is flipped horizontally orvertically before used to predict current block), or line based intrablock copy (each compensation unit inside an M×N coding block is an M×1or 1×N line).

FIG. 7 shows an example of intra block copy according to an embodimentof the disclosure. Current picture (700) is under decoding. The currentpicture (700) includes a reconstructed area (710) (grey area) andto-be-decoded area (720) (white area). A current block (730) is underreconstruction by a decoder. The current block (730) can bereconstructed from a reference block (740) that is in the reconstructedarea (710). The position offset between the reference block (740) andthe current block (730) is referred to as a block vector (750) (or BV(750)).

In some implementation examples, the reconstructed samples of thecurrent picture can be buffered in a dedicated memory. In considerationof the implementation cost, the reference area cannot be as large asfull frame, but up to the memory size of the dedicated memory. In someembodiments, the block vector in the intra block copy is allowed torefer to only some neighboring area, but not the whole picture. In oneexample, the memory size of the dedicated memory is one CTU, then whenthe reference block is within the same CTU as the current block, theintra block copy mode can be used. In another example, the memory sizeis two CTUs, then when the reference block is either within the currentCTU, or the CTU to the left of current CTU, the intra block copy modecan be used. When the reference block is outside the designated localarea, even the reference block has been reconstructed, the referencesamples cannot be used for intra picture block compensation in anexample.

With the constrained reference area, the efficiency of intra block copyis limited. There is a need to further improve the efficiency of intrablock copy with a constrained reference area.

In some versions of video coding standard, such as in a version of VVC,a picture is divided into an array of non-overlapped CTUs. The size of aCTU is set to be 128×128 luma samples (and the corresponding chromasamples depending on the color format). A CTU can be split into CodingUnits (CU) using one or a combination of the tree splitting methods,such as a binary-tree (BT) split, a ternary-tree (TT) split, and thelike. A BT split divides a parent block in half in either horizontal orvertical direction. The resulting two smaller partitions of the BT splitare half in size as compared to the parent block. A TT split divides theparent block into three parts in either horizontal or verticaldirection. The middle part of the three is twice as large as the othertwo parts. The resulting three smaller partitions of the TT split are ¼,½ and ¼ in size as compared to the parent block.

In some embodiments, the partitions of a block at 128×128 level areconstrained to allow certain results, such as one 128×128 block, two128×64 blocks, two 64×128 blocks or four 64×64 blocks. In some examples,the partitions are further constrained such that at block level of128×64 or 64×128, the TT splits at either (horizontal or vertical)direction are not allowed. In addition, in an example, the 128×64 or64×128 are only allowed to be split into two 64×64 blocks when there isany further split. The constrained partitioning types are referred to asregular partitioning types.

In some examples, intra block copy is implemented with limited memoryrequirement. In implementation example, the designated memory to storereference samples of previously coded CUs for future intra block copyreference is referred to as reference sample memory. For example, themaximum size of a reference sample memory (also referred to as a buffer)that is used to store unfiltered samples for intra block copy mode is 1CTU (128×128 luma samples and corresponding chroma samples) size. Inorder to fully utilize such a constrained memory, in some examples, thebuffer is updated on 64×64 basis. When some parts of the referencesample memory has not yet been updated with reconstructed samples fromthe current CTU, the data stored in those parts of memory are actuallythe reconstructed samples from the left CTU in an example. These samplesmay be used as a reference for predicting the current block in intrablock copy mode. Then, the effective search range is extended fromwithin the current CTU to some part of the left CTU.

Thus, in some embodiments, the reference sample memory can be reused tostore previous coded samples in the left CTU, before the referencesample memory is updated with reconstructed samples in the current CTU.In an embodiment, the availability of the reference sample memory isupdated on a 64×64 basis. In an example, if any of the reference samplesin a 64×64 block has been updated, the entire 64×64 block is consideredas being updated with reconstructed samples from the current CTU andwill no longer be considered as storing samples before the update. Insome implementation examples, a continuous memory space in a memory(e.g., buffer memory, on chip memory, and the like) are allocated tostore reconstructed samples of the 64×64 block, the address operationsfor storing and reading-back the reconstructed samples from thecontinuous memory space can be performed with relatively easycalculations. In some examples, the continuous memory space that storesthe reconstructed samples of a coding region, such as the 64×64 codingregion, is referred to as memory update unit. Accessing samples in amemory update unit can be performed with reduced address calculations,and accessing samples in different memory update units can requireincreased number of address calculations.

FIGS. 8A-8D show examples of reference sample memory updates on 64×64basis, and effective search ranges for the intra block copy modeaccording to an embodiment of the disclosure. In some examples, anencoder/decoder includes a cache memory that is able to store samples ofone CTU, such as 128×128 samples. Further, in the FIGS. 8A-8D examples,a CTU is divided into four 64×64 coding regions. The coding regionhaving a current block (may be equal to or smaller than the codingregion) for prediction is referred to as a current coding region(labeled as “Curr”). It is noted that the examples can be suitablymodified for coding regions of other suitable sizes.

Each of FIGS. 8A-8D shows a current CTU (820) and a left CTU (810). Theleft CTU (810) includes four coding regions (811)-(814), and each codingregion has a sample size of 64×64 samples. The current CTU (820)includes four coding regions (821)-(824), and each coding region has asample size of 64×64 samples. The current CTU (820) is the CTU thatincludes a current coding region (as shown by a label “Curr” and withvertical stripe pattern) under reconstruction. The left CTU (810) is theimmediate neighbor on the left side of the current CTU (820). It isnoted in FIGS. 8A-8D, the grey blocks are coding regions that arealready reconstructed, and the white blocks are coding regions that areto be reconstructed.

In FIG. 8A, the current coding region under reconstruction is the codingregion (821). The cache memory stores reconstructed samples in thecoding regions (812), (813) and (814), and the cache memory will be usedto store reconstructed samples of the current coding region (821). Inthe FIG. 8A example, the effective search range for the current codingregion (821) includes the coding regions (812), (813) and (814) in theleft CTU (810) with reconstructed samples stored in the cache memory. Inan example, when the cache memory is updated with one or morereconstructed samples from the current coding region (821), thus thecoding region (811) is considered as not available (marked with “X”) inthe cache memory for CPR prediction due to the fact that some part ofthe coding region (811) has been updated by the reconstructed samplesfrom the current CTU. It is noted that, in an embodiment, thereconstructed samples of the coding region (811) are stored in a mainmemory (e.g., are copied from the cache memory to the main memory beforethe reconstruction of the coding region (821)) that has a slower accessspeed than the cache memory.

In FIG. 8B, the current coding region under reconstruction is the codingregion (822). The cache memory stores reconstructed samples in thecoding regions (813), (814) and (821), and the cache memory will be usedto store reconstructed samples of the current coding region (822). Inthe FIG. 8B example, the effective search range for the current codingregion (822) includes the coding regions (813) and (814) in the left CTU(810) and (821) in the current CTU (820) with reconstructed samplesstored in the cache memory. In an example, when the cache memory isupdated with one or more reconstructed samples from the current codingregion (822), thus the coding region (812) is considered as notavailable (marked with “X”) in the cache memory for CPR prediction dueto the fact that some part of the coding region (812) has been updatedby the reconstructed samples from the current CTU. It is noted that, inan embodiment, the reconstructed samples of the coding region (812) arestored in a main memory (e.g., are copied from the cache memory to themain memory before the reconstruction of the coding region (822)) thathas a slower access speed than the cache memory.

In FIG. 8C, the current coding region under reconstruction is the codingregion (823). The cache memory stores reconstructed samples in thecoding regions (814), (821) and (822), and the cache memory will be usedto store reconstructed samples of the current coding region (823). Inthe FIG. 8C example, the effective search range for the current block(823) includes the coding regions (814) in the left CTU (810) and (821)and (822) in the current CTU (820) with reconstructed samples stored inthe cache memory. In an example, when the cache memory is updated withone or more reconstructed samples from the current coding region (823),thus the coding region (813) is considered as not available (marked with“X”) in the cache memory for CPR prediction due to the fact that somepart of the coding region (813) has been updated by the reconstructedsamples from the current CTU. It is noted that, in an embodiment, thereconstructed samples of the coding region (813) are stored in a mainmemory (e.g., are copied from the cache memory to the main memory beforethe reconstruction of the coding region (823)) that has a slower accessspeed than the cache memory.

In FIG. 8D, the current coding region under reconstruction is the codingregion (824). The cache memory stores reconstructed samples in thecoding regions (821), (822) and (823), and the cache memory will be usedto store reconstructed samples of the current coding region (824). Inthe FIG. 8D example, the effective search range for the current codingregion (824) includes the blocks (821), (822) and (823) in the currentCTU (820) with reconstructed samples stored in the cache memory. In anexample, when the cache memory is updated with one or more reconstructedsamples from the current coding region (824), thus the coding region(814) is considered as not available (marked with “X”) in the cachememory for CPR prediction due to the fact that some part of the codingregion (814) has been updated by the reconstructed samples from thecurrent CTU. It is noted that, in an embodiment, the reconstructedsamples of the coding region (814) are stored in a main memory (e.g.,are copied from the cache memory to the main memory before thereconstruction of the coding region (824)) that has a slower accessspeed than the cache memory.

It is noted that in the FIGS. 8A-8D example, a total memory of 4×64×64luma samples (together with corresponding chroma samples) is used forintra block copy compensation. The technique used in the FIGS. 8A-8Dexample can be suitably modified for other memory sizes, such as totalmemory of 3×64×64, 2×64×64 luma samples.

It is noted that, in some embodiments, ternary tree partitioning at128×128 level and lower is allowed, and the partition results can benon-square blocks.

In some examples, at 128×128 level, a CTU can be partitioned usingternary-tree split. For a horizontal TT split, the resulting blocks ofpartition will be 128×32, 128×64 and 128×32. For a vertical split, theresulting blocks of the partition will be 32×128, 64×128 and 32×128.

Further, in some examples, at 128×64/64×128 level, ternary-tree splitcan be used and resulting blocks can be non-square blocks.

FIGS. 9A-9H show some examples of partitions that can result innon-square blocks.

According to some aspects of the disclosure, some partition types, suchas the TT split at 128×128 level, and the like that can result in acoding block that cannot be contained in a 64×64 coding region or cannotcontain one or more 64×64 coding region. These partition types arereferred to as flexible partition types.

When these flexible partition types are allowed on top of those regularpartition types. The reference sample update process may no longer bealigned with 64×64 coding regions one by one. There is a need to developmethods to enable the reference sample memory buffer reuse strategy asmentioned above.

According to an aspect of the disclosure, certain reference areaconstraints can be used to improve intra block copy performance. Morespecifically, in an example, the location of a reference sample block inthe reference sample memory is constrained, to be within the same 64×64coding region. In some embodiments, the size of reference sample memoryis fixed to be two 64×64 luma samples (together with correspondingchroma samples). It is noted that the techniques used in the presentdisclosure can be suitably modified to use for different referencesample memory sizes, such as using three 64×64 luma samples pluscorresponding chroma samples, four 64×64 luma samples plus correspondingchroma samples (i.e. 1 CTU size), etc.

Generally, the size of an IBC coded block can be as large as any regularinter coded block. According to an aspect of the present disclosure, inorder to utilize the reference sample memory more efficiently, the sizeof an IBC coded block is limited. In an example, the size of an IBCcoded block is limited not to be larger than higher limits, such as 64luma samples at either width or height (with corresponding sizeconstraints applied to chroma samples, depending on the color format;e.g., in 4:2:0 format, the size of a chroma block in IBC mode should notbe larger than 32 samples each side). Further, in some examples, thesize of an IBC coded block is limited no to be lower than lower limits,such as 32 luma samples at either width or height. While maximum IBCsize of 64×64 luma samples is used in description, it is noted that thetechniques can be suitably modified for other maximum IBC size.

In the following description, the maximum size of the reference samplememory that is be used to store intra block copy reference samplescorresponds to the memory size for storing two 64×64 luma samples andcorresponding chroma samples.

According to some aspects of the disclosure, the reference sample memoryhas a size for storing sample information of two coding regions, eachcoding region has a size of 64×64 luma samples, and the sampleinformation includes luma sample information of the 64×64 luma samplesand chroma sample information of the corresponding chroma samples. Then,the reference sample memory stores sample information of a currentcoding region in the current CTU, and sample information of anothercoding region that is one of some previously coded 64×64 coding regions.

FIGS. 10A and 10B show two examples of coding orders and referencesample memory usage. In FIGS. 10A and 10B, the regions with grey colorare coding regions (e.g., 64×64 luma samples) that have been coded; theregions with white color are regions that have not yet been coded; andthe region(s) with the slant lines are the coding region(s) where thecurrent coding block is located. Further, in FIGS. 10A and 10B, the twocoding regions in the reference sample memory are shown in dottedbox(es).

In FIG. 10A, in an example, a CTU is under horizontal binary split orquad-tree split at 128×128 level. Then, the coding order of 64×64 codingregions follows (1001) to (1004).

In FIG. 10B, in an example, a CTU is under vertical binary split at128×128 level. Then, the coding order of 64×64 coding regions follows(1011) to (1014).

For the examples in FIGS. 10A and 10B, when the current coding block islocated in one of the four 64×64 coding regions in the current CTU, thereference sample memory can store another 64×64 coding region that isassigned to be the reference of intra block copy mode.

It is noted that FIGS. 10A and 10B are merely examples, other possiblereference area assignments are also possible. In an embodiment, thetop-right 64×64 coding region is used as the reference area for thebottom-right 64×64 coding region as shown in FIGS. 10A and 10B. Inanother embodiment, the top-left 64×64 coding region is used as thereference area for the bottom-right 64×64 coding region.

Ideally, reconstructed samples in the reference sample memory can beused for predicting current block in intra block copy mode. However,sometimes samples in a reference block may come from two different 64×64coding regions.

FIGS. 11A and 11B show examples of samples in a reference block comingfrom two different 64×64 coding regions. In FIG. 11A, part of thereference block comes from one 64×64 coded coding region while anotherpart, although already reconstructed, belongs to another 64×64previously coded coding region. In FIG. 11B, part of the reference blockcomes from one 64×64 coded region while another part, although alreadyreconstructed, belongs to current 64×64 coding region. Because each ofthe 64×64 coding regions in the reference sample memory will be operatedseparately, the two 64×64 coding regions in memory may not be physicallyconnected. These positions of a reference block in different codingregions, such as shown in FIGS. 11A and 11B may bring extra memoryaccess or operations, which is not desirable.

According to some aspects of the disclosure, additional constrains areused with other suitable block vector constraints that make intra blockcopy work in a particular video/image coding system. The additionalconstrains are imposed on the block vector of intra block copy mode,such that the whole reference block for intra block copy mode should belocated inside the same 64×64 coding region. The 64×64 coding regionrefers to the fact that each CTU with 128×128 luma samples (pluscorresponding chroma samples) can be divided into 4 non-overlapped 64×64regions. Each of these 64×64 regions is considered as the 64×64 codingregion in the constraints in some examples.

In an embodiment, the top left corner of a reference block is denoted as(Ref_TLx, Ref_TLy); the bottom right corner of a reference block isdenoted (Ref_BRx, Ref_BRy) assuming the top-level corner of the CTU is(0, 0) for example. The additional constrains is in the form ofbitstream conformance requirements that the following conditions (Eq. 1)and (Eq. 2) shall be met:Ref_BRx/64=Ref_TLx/64  (Eq. 1)Ref_BRy/64=Ref_TLy/64  (Eq. 2)

When (Eq. 1) is satisfied, the integer portion of Ref_BRx/64 is equal tothe integer portion of Ref_TLx/64. When (Eq. 2) is satisfied, theinteger portion of Ref_BRy/64 is equal to the integer portion ofRef_TLy/64. It is noted the division operations can be performed byright shifting of 6 bits.

In some embodiments, when a block vector points to a reference blocklocation, where not all the samples in this reference block belong tothe same 64×64 coding region, the block vector can be clipped to anearby reference block location that meets the same 64×64 coding regionrequirement. In an embodiment, the clipping refers to move the originalreference block location (which covers at least two 64×64 regions)towards one direction vertically or horizontally. In an example, themoving is in a direction to reduce the distance between the referenceblock and current block. Also, the moving is in a direction to increasethe percentage of reference samples that belong to the same 64×64 sampleregion and eventually make the whole reference block belong to the same64×64 region.

In a case of the example shown in FIG. 11A, the reference block can bemoved vertically up until all samples belong to the top 64×64 codingregion. It is noted that, in FIG. 11A example, moving the referenceblock downward can increase the distance between two blocks and movingthe reference block horizontally does not change the percentage ofsamples in each 64×64 coding region.

In a case of the example shown in FIG. 11B, the reference block can bemoved horizontal right until all samples belong to the current 64×64coding region. It is noted that, in the FIG. 11B example, moving thereference block leftward can increase the distance between two blocks;and moving vertically does not change the percentage of samples in each64×64 coding region.

In some embodiments, when a block vector points to a reference blocklocation, where not all the samples in this reference block belong tothe same 64×64 coding region, the samples outside the 64×64 codingregion may be generated by sample padding (vertically and/orhorizontally duplicate the samples on the boundary of the 64×64 codingregion). The padding process can be performed in the similar manner asborder extension for reference picture in motion compensation.

In an example, the top left corner of a reference block is located is ina 64×64 coding region, and then the 64×64 coding region is considered aswhere the coding region the reference block should come from. If anypart of the reference block is outside that coding region, padding canbe used to determine the samples of that part.

In another example, the bottom right corner of the reference block islocated in a 64×64 coding region, and then the 64×64 coding region isconsidered as where the reference block should come from. If any part ofa reference block is outside that coding region, padding can beperformed to determine the samples of that part.

In another example, the top left corner of the reference block islocated in a 64×64 coding region, and the 64×64 coding region is usedfirst to determine which coding region the reference block comes from.When the location is not a valid reference location, then the bottomright corner of the reference block is considered to determine whichcoding region the reference block comes from.

In another example, the bottom right corner of the reference block islocated in a 64×64 coding region, and the 64×64 coding region is usedfirst to determine which coding region the reference block comes from.If the location is not a valid reference location, then the top leftcorner of the reference block is considered to determine which codingregion the reference block comes from.

In another embodiment, when a block vector points to a reference blocklocation, where all the samples in the reference block are outside thevalid reference region (either current 64×64 coding region or previouslycoded 64×64 coding region(s)), the samples outside the 64×64 codingregion may be generated by sample padding (vertically and/orhorizontally duplicate the samples on the boundary of the closest validreference region. The padding process may be performed in the samemanner as border extension for reference picture in motion compensation,where the border can be regarded as the boundary of the allowedreference region(s).

Aspects of the disclosure also provide flexible block partitioningstrategies and the buffer reuse mechanism for intra block copy.

In some embodiments, when intra block copy is used for a given codinglevel (such as for a sequence, for a picture or for a slice/tile/tilegroup), the flexible block partition types, such as 128×32/32×128,cannot be used.

In an embodiment, for a given coding level (such as for a sequence, fora picture or for a slice/tile/tile group), when the flexible blockpartition types are not used, intra block copy mode can use thereference sample memory reuse strategies. For example, the 64×64 codingregion based update process and buffer reuse strategies can be used.

In an embodiment, for a given coding level (such as for a sequence, fora picture or for a slice/tile/tile group), when the flexible blockpartition types are in use, intra block copy mode cannot use referencesample memory reuse strategies disclosed in the above disclosure.Instead, in an example, the block vector is restricted to refer toreconstructed parts of the current CTU.

In an embodiment, for a given coding level (such as for a sequence, fora picture or for a slice/tile/tile group), when the above-mentionedflexible block partition types are in use, the above-mentioned referencesample memory reuse strategies may be modified.

In some examples, when coding blocks are in the first TT partition(e.g., left 32×128 or top 128×32), or BT partition (top 128×64 or left64×128) or QT partition (top-left 64×64) at CTU (128×128) level, aportion of reference samples in the left CTU can be used.

FIGS. 12A-12F show examples of reference samples memory reusestrategies. In each of the FIGS. 12A-12F examples, the current codingblock is shown by slant lines, and the available reference area is shownby grey color.

In an example, the top-right corner 64×64 (samples) region in the leftCTU is the available reference area, as shown by grey color in theexamples of FIGS. 12A-12C.

In another example, the right most 32×128 (samples) region in the leftCTU is the available reference area, as shown by grey color in theexamples of FIGS. 12D-12F.

In another example, the top 128×32 region in the left CTU is theavailable reference area.

In another example, the choice of a region is determined by thepartitions of the left CTU. For example, when the left CTU uses quadtreepartition at 128×128 level, then the top-right 64×64 (samples) region inthe left CTU may be used to predict coding block in the first partitionof current CTU.

In another example, when a total of 3×64×64 sized memory is used, for acoding block in the first partition of the current CTU, the size ofmemory that can be used to store reference samples from the left CTU is64×64 in size (not necessarily to be a square). It is noted that thememory space is not necessarily to store the samples in a square shape.

In another embodiment, when a total 4×64×64 sized memory is used, for acoding block in the first partition of current CTU, the size of memorythat can be used to store reference samples from the left CTU is 2×64×64in size (not necessarily to be a two squares). It is noted that thememory space is not necessarily to store the samples in two squares.

In some embodiments, when flexible block partition types and intra blockcopy mode are both used in a given coding level (such as for a sequence,for a picture or for a slice/tile/tile group), techniques are used toreuse the reference sample memory so that the search range of intrablock copy can be effectively increased while the memory requirement iskept the same or reduced.

In some examples, a smaller or same granularity update process with moreblock shapes can be proposed, such as in the shapes of 32×32 or 32×64 or64×32 or 16×128, instead of using 64×64 based update process previously.In an example, the update process can use 32×32 (samples) unit, and thecurrent CTU is partitioned using TT at 128×128 level.

FIGS. 13A-13C show an example of an update process that uses 32×32(samples) unit, and FIGS. 13D-13F show another example of an updateprocess that uses 32×32 (samples). Each 32×32 (samples) unit is shown asa small square. In the FIGS. 13A-13F examples, the reference samplememory size is 128×128 in total. Then, a first memory space of 3×64×64samples is allocated to store samples that can be reference samples forintra block copy reference purpose, and a second memory space of 64×64samples is allocated for the current 64×64 sized unit (not necessarilyto be a square, the total number of luma samples is equal to 64×64samples). For each 64×64 or 64×128 sized partition and itssub-partitions (not necessary to be square, the total number of lumasamples is equal to 64×64), the reconstructed samples in the current CTUand some other previously coded regions, such as indicated by the greyareas in FIG. 13A-13F can be stored in the reference sample memory andcan be referred for the intra block copy prediction.

FIG. 14 shows a flow chart outlining a process (1400) according to anembodiment of the disclosure. The process (1400) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1400) are executed by processing circuitry,such as the processing circuitry in the terminal devices (110), (120),(130) and (140), the processing circuitry that performs functions of thevideo encoder (203), the processing circuitry that performs functions ofthe video decoder (210), the processing circuitry that performsfunctions of the video decoder (310), the processing circuitry thatperforms functions of the video encoder (403), and the like. In someembodiments, the process (1400) is implemented in software instructions,thus when the processing circuitry executes the software instructions,the processing circuitry performs the process (1400). The process startsat (S1401) and proceeds to (S1410).

At (S1410), prediction information of a current block is decoded from acoded video bitstream. The prediction information is indicative of intrablock copy mode.

At (S1420), a block vector that points to a reference block in the samepicture as the current block is determined.

At (S1430), the reference block is checked to determine whether thereference block is completely within a coding region. In someembodiments, a reference sample memory having a limited storage space isreused to store previous coded samples. For example, before thereference sample memory is updated with reconstructed samples in thecurrent CTU, the reference sample memory stores samples in the left CTUof the current CTU. The reference sample memory is updated withreconstructed samples in the current CTU in the unit of coding region.In an embodiment, the availability of the reference sample memory isupdated on a 64×64 basis. In an example, if any of the reference samplesin a 64×64 block has been updated, the entire 64×64 block is consideredas being updated with reconstructed samples from the current CTU andwill no longer be considered as storing samples before the update. In anembodiment, a CTU of 128×128 samples includes four 64×64 regions thatcan be referred to as coding regions.

In an embodiment, multiple corners of the reference block are checked todetermine whether the reference block is completely within a codingregion. When the reference block is completely in the coding region, theprocess proceeds to (S1450); otherwise, the process proceeds to (S1440).

At (S1440), the reference block is suitably restricted in the codingregion. In some embodiments, the reference block is suitably moved intothe coding region. In some embodiments, some reference samples that arenot in the coding region can be padded with other reference samples thatare in the coding region. Then, the memory access to retrieve thereference samples for reconstruction of the current block can beachieved by accessing only one memory update unit in an example.

At (S1450), the current block is reconstructed based on thereconstructed samples of the reference block that are retrieved from thereference sample memory. For example, the reference sample memory isaccessed to retrieve the reconstructed samples of the reference block,and then samples of the current block are reconstructed based on thereconstructed samples that are retrieved from the reference samplememory. Because the reference block is restricted that reference samplesof the reference block are completely in one coding region, or can bedetermined based on one coding region, then address operations forretrieving the reference samples can be performed with ease and highefficiency. Then the process proceeds to (S1499) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 15 shows a computersystem (1500) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 15 for computer system (1500) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1500).

Computer system (1500) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1501), mouse (1502), trackpad (1503), touchscreen (1510), data-glove (not shown), joystick (1505), microphone(1506), scanner (1507), camera (1508).

Computer system (1500) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1510), data-glove (not shown), or joystick (1505), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1509), headphones(not depicted)), visual output devices (such as screens (1510) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1500) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1520) with CD/DVD or the like media (1521), thumb-drive (1522),removable hard drive or solid state drive (1523), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1500) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1549) (such as, for example USB ports of thecomputer system (1500)); others are commonly integrated into the core ofthe computer system (1500) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1500) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1540) of thecomputer system (1500).

The core (1540) can include one or more Central Processing Units (CPU)(1541), Graphics Processing Units (GPU) (1542), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1543), hardware accelerators for certain tasks (1544), and so forth.These devices, along with Read-only memory (ROM) (1545), Random-accessmemory (1546), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1547), may be connectedthrough a system bus (1548). In some computer systems, the system bus(1548) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1548),or through a peripheral bus (1549). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1541), GPUs (1542), FPGAs (1543), and accelerators (1544) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1545) or RAM (1546). Transitional data can be also be stored in RAM(1546), whereas permanent data can be stored for example, in theinternal mass storage (1547). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1541), GPU (1542), massstorage (1547), ROM (1545), RAM (1546), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1500), and specifically the core (1540) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1540) that are of non-transitorynature, such as core-internal mass storage (1547) or ROM (1545). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1540). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1540) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1546) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1544)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information of a current block of acurrent coding region in a coded video bitstream, the predictioninformation being indicative of an intra block copy mode; determining ablock vector that points to a reference block in a same picture as thecurrent block, the reference block being located within a search range,the search range including reconstructed samples of coding regionscomprising a coding tree unit (CTU) of the current block andreconstructed samples of at least one coding region comprising a CTUadjacent to the CTU of the current block; reconstructing at least asample of the current block based on reconstructed samples of thereference block ; and updating the search range for reconstruction of anext coding region such that reconstructed samples of the current blockare included in the updated search range and the reconstructed samplesof the at least one coding region comprising the CTU adjacent to the CTUof the current block are not available in the updated search range. 2.The method of claim 1, wherein each coding region has a square shape. 3.The method of claim 1, wherein each CTU is configured to have 128samples by 128 samples of a luma component.
 4. The method of claim 1,wherein the search range is updated in a unit of one coding region. 5.The method of claim 1, further comprising: checking whether multiplecorners of the reference block are within a coding region.
 6. The methodof claim 5, wherein each CTU contains 128×128 luma samples and eachcoding region is 64×64 luma samples in size.
 7. The method of claim 5,wherein each CTU contains less than 128×128 luma samples and each codingregion is the same as the CTU in size.
 8. The method of claim 1, furthercomprising: moving the reference block into the search range when thereference block is partially in the search range before the moving. 9.The method of claim 8, further comprising: moving the reference block ina direction to reduce a distance between the reference block and thecurrent block.
 10. The method of claim 8, further comprising: moving thereference block in a direction that increases a percentage of referencesamples in a coding region.
 11. The method of claim 1, furthercomprising: using information of a first reference sample that is in thesearch range as information of a second reference sample that is out ofthe search range when the reference block is partially in the searchrange.
 12. The method of claim 1, wherein flexible block partition isprohibited as a partition of each CTU.
 13. An apparatus of videodecoding, comprising: processing circuitry configured to: decodeprediction information of a current block of a current coding region ina coded video bitstream, the prediction information being indicative ofan intra block copy mode; determine a block vector that points to areference block in a same picture as the current block, the referenceblock being located within a search range, the search range includingreconstructed samples of coding regions comprising a coding tree unit(CTU) of the current block and reconstructed samples of at least onecoding region comprising a CTU adjacent to the CTU of the current block;reconstruct at least a sample of the current block based onreconstructed samples of the reference block; and updating the searchrange for reconstruction of a next coding region such that reconstructedsamples of the current block are included in the updated search rangeand the reconstructed samples of the at least one coding regioncomprising the CTU adjacent to the CTU of the current block are notavailable in the updated search range.
 14. The apparatus of claim 13,wherein each coding region has a square shape.
 15. The apparatus ofclaim 13, wherein each CTU is configured to have 128 samples by 128samples of a luma component.
 16. The apparatus of claim 13, wherein thesearch range is updated in a unit of one coding region.
 17. Theapparatus of claim 13, wherein the processing circuitry is furtherconfigured to: check whether multiple corners of the reference block arewithin a coding region.
 18. The apparatus of claim 17, wherein each CTUcontains 128×128 luma samples and each coding region is 64×64 lumasamples in size.
 19. The apparatus of claim 17, wherein each CTUcontains less than 128×128 luma samples and each coding region is thesame as the CTU in size.
 20. The apparatus of claim 13, wherein theprocessing circuitry is further configured to: move the reference blockinto the search range coding region when the reference block ispartially in the search range before the moving.